1. Field
The invention relates to the field of microdispensing systems for open-jet dispensing of liquids.
2. Description
Open-jet dispensing systems consist of a dispensing nozzle, a liquid supply line to the dispensing nozzle, and a dispensing drive.
Different operating principles are known for the dispensing drive in microdispensing systems and piezo-actors, bubble-jet actors, electrostatic, pneumatic and magnetostrictive drives are in practical use. Important uses of these drives are in inkjet printing and micropipetting.
For dispensing biological liquids and suspended cells it is important that no or minimal shearing forces, pressure and temperature influences occur. The waste heat of known electromechanical drives can have an adverse effect on the stability of protein and enzyme solutions during dispensing. Consequently, known drives can be used only to a limited degree.
Moreover, before dispensing most known microdispensing systems have to be vented and initialized by dispensing runs. After dispensing, each microdispensing system must be emptied, flushed and cleaned. Because it is extraordinarily important to use sparingly the usually expensive liquids and because known microdispensing systems can be initialized, emptied or flushed only by a large number of dispensing runs with repeated drive actuation followed by completely discarding the excess liquid, recovery of liquid is nearly impossible.
Cleaning can be a considerable problem in microdispensing systems, especially the dispensing nozzle. Depending on the type of construction, the nozzle cannot be interchanged, making cleaning difficult in the event of contamination or any clogging.
In addition, most known dispensing systems are not made completely from inert materials. In known electromechanical dispensing systems, the drive is often subjected to liquid for dispensing flowing around it. Apart from the mentioned heating problem, this can lead to contamination of the liquid and incorrect drive operation due to soiling.
Another disadvantage of known open-jet dispensing systems is that the quantity dispensed per run is predetermined by the construction and is influenced by the viscosity and surface tension of the liquid for dispensing. In view of the above problems, there has been a long felt need for an invention that addresses these concerns.
The subject invention provides a microdispensing system for open-jet dispensing a liquid. This system comprises a valve, at least one liquid supply line, an outlet, a dispensing nozzle, an actuator chamber, and an electromechanical drive. The valve has a chamber that is formed at least in part from a liquid-impermeable elastic membrane that can be stretched from a resting position to a stretched position. The valve chamber is filled with the liquid to be dispensed. At least one liquid supply line is in liquid communication with the valve chamber. This at least one supply line is configured and dimensioned for supplying liquid to the valve chamber. The outlet is open to liquid communication with the valve chamber when the elastic membrane is in the stretched position C losed to liquid communication with the valve chamber when the elastic membrane is in the resting position. The outlet is configured and dimensioned so that when the elastic membrane is in the stretched position, liquid from the valve chamber enters the outlet. The dispensing nozzle is configured and dimensioned to be in liquid communication with the outlet and to open-jet dispense liquid. The dispensing nozzle is constructed so that when liquid flows from the outlet into the dispensing nozzle, it is open-jet dispensed from the dispensing nozzle. The actuator chamber located adjacent the elastic membrane on the side of the membrane opposite the valve chamber. The actuator chamber is configured and dimensioned to be pressure-tight and to retain a pressure differing from atmospheric pressure. The electromechanical drive is located within the actuator chamber and is connected to the membrane. The electromechanical drive is constructed so that when actuated, it stretches the membrane from the resting position to the stretched position, thereby allowing liquid from the valve chamber to enter the outlet and to be open-jet dispensed through the dispensing nozzle.